Recently, demands for flat display devices represented by a liquid crystal display, which takes advantage of the slim, lightweight, and low power consumption features, are rapidly growing. Above all, an active matrix type display device, which includes, in each pixel, a pixel switch having a function of electrically isolating an on pixel and an off pixel and maintaining a video signal to the on pixel, is utilized for various displays, such as a portable information device.
As such flat active matrix type display device, an organic EL display device which uses a self-luminous element is receiving attention, and research and development of this type of device have been conducted vigorously. The organic EL display device has the features that it requires no backlight, is suitable for moving image reproduction by virtue of high-speed response, and is suitable for use even in a cold district since luminance does not decrease at low temperatures.
Generally, the organic EL display device comprises a plurality of pixels arranged side by side over a plurality of lines and rows. Each of the pixels comprises an organic EL element, which is a self-luminous element, and a pixel circuit which supplies a driving current to the organic EL element. Each of the pixels performs a display operation by controlling emission brightness of the organic EL element.
As a method of driving a pixel circuit, performing the driving by a voltage signal is known. Further, proposals are made for a display device which achieves the high-definition property. That is, by structuring a display device such that “Low” and “High” are switched by switching of a voltage power source, and both a video signal and an initialization signal are output from video signal wiring, the number of constituent element pixels and the number of wiring lines are reduced, and a layout area of the pixel is also reduced. Based on this structure, a proposal for a high-definition display device is made.